Razor blade of a chromium containing steel

ABSTRACT

A RAZOR BLADE MADE OF A CHROMIUM STAINLESS STEEL HAVING GOOD CORROSION RESISTANCE AND CUTTING PROPERTIES AND ALSO A METHOD FORMING SUCH AN ARTICLE IS DICLOSED. THE STEEL CONTAINS .30-45 CARBON, 11-16 CR, A MEMBER OF THE CLASS CONSISTING OF TUNGSTEN AND MOLYBDENUM WHEREIN THE AMOUNT OF MO MAY BE .5-2.5% AND W1.0-5%, SI MAX. 70, MN 1.5 MAX., 0-2% OF VA, TA, TI AND ZR AND 0-1% CO, NI, CU, AL, BE AND B. THE STELL MAY BE FORMED BY COLD ROLLING, HARDENING BY HEATING TO A RANGE OF 10001150*C. SUBSEQUENT TEMPERING MAY BE UTILIZED.

.IuIy 27, 197T J. IF. mmmfi mm... 3595 643 RAZOR BLADE OF A CHROMIUMCONTAINING STEEL Filed June 10, 1966 STRESS CORROSION SENSITIVITY HIGHINTER MEDIATE LOW PERCENT CARBON 3,595,643 RAZOR BLADE OF A CHROMHUMCONTATNlNG STEEL Joseph F. Boyce, Braintree, Mass, and Axel VilhelmBernstein and Jan-Christen- Henric Uvesson (Iarln, Sandviken, Sweden,assignors to Sandvikens .llernverlm Aktiebolag, Sandviken, Sweden FiledJune 10, 1966, Ser. No. 556,691 Int. Cl. CZZc 33/00 US. Cl. 75-126C 3Claims ABSTRACT OF THE DISCLOSURE A razor blade made of a chromiumstainless steel having good corrosion resistance and cutting propertiesand also a method forming such an article is disclosed. The steelcontains .30.45 carbon, 11-16 Cr, a member of the class consisting oftungsten and molybdenum wherein the amount of Mo may be .52.5% and W1.05%, Si max. 70, Mn 1.5 max., 02% of Va, Ta, Ti and Zr and 0-1% Co,Ni, Cu, Al, Be and B. The steel may be formed by cold rolling, hardeningby heating to a range of 1000- 1150 C. Subsequent tempering may beutilized.

The present invention relates to razor blades especially in the form ofthin ribbon-like razor blades, and similar thin elongated sharp edgedblades having very good corrosion resistance and cutting properties andsimultaneously being able to withstand stress corrosion or hydrogeninduced failures when subjected to severe bending stresses. Theribbon-like razor blades are for instance used in a razor where a thinstrip successively can be fed from one roll to another for changing thecutting edge. When used in this way the steel is subjected to highbending stresses and a simultaneous chemical attack of a relatively longduration, which requires a high resistance to stress corrosion to avoidruptures. The steel must also provide very good cutting edges aftergrinding. Previously known steels have not had the desired combinationof properties. The steel according to the invention has a compositionwhich in combination with a suitable heat treatment provides the desiredcorrosion resistance and flexibility, at the same time having hardnesssatisfactorily high for obtaining a sufficient sharpness and wearresistance of the cutting edge.

The phenomenon which above has been referred to as stress corrosion isnot wholly clarified. In certain cases the cause of rupture isconsidered to be what normally is called stress corrosion. In othercases it seems obvious that the ruptures are caused by hydrogenabsorption and embrittlement. In the following we refer to the actualrupture phenomenon as stress corrosion without regard to which of thesaid explanations is correct.

Previously known steels of the type containing 18% chromium and 8%nickel, cold worked and heat treated to a high hardness (as for instancedescribed in UK Pat. No. 979,512) have shown a low sensitivity to stresscorrosion, but they contain a high percentage of residual austenitewhich causes difficulties in finishing the cutting edge or edges. Inorder to avoid said and other difiiculties and drawbacks of the previoussteel alloys used for the purpose mentioned, the present inventionprovides razor blades and similar thin elongated sharp edged blades madeof a stainless martensitic chromium steel having, for a razor bladesteel, a very low content of carbon and containing molybdenum and/ortungsten which have been found necessary to improve the importantproperties, such as corrosion resistance and stress corrosionresistance.

Further details of the invention appear from the follow ingspecification and the appended drawing which shows, in the form of adiagram, resistance to stress corrosion in 3,95,643 Patented July 27,1971 relation to hardness by steels according to the invention and asimilar steel Without molybdenum.

The razor blades according to the present invention are characterized byvery good cutting properties, high corrosion resistance and toughnessand high resistance to ruptures at blending stresses exceeding 71,000psi. under simultaneous chemical attack, e.g. of the type found inlocations in which razors are used and/or stored. The blades areconsequently made of a steel having the following analysis: 0.30-0.45%carbon; 11-16% chromium; 0.5-2.5% molybdenum, or 1.05.0% tungsten, or amixture of molybdenum and tungsten in an amount such that the sum ofmolybdenum and one-half of the tungsten is 0.5-2.5%; 00.70% silicon;0-1.5% manganese and the rest iron with incidental impurities. Whilevery small amounts of additional carbide formers, such as vanadium,niobium, tantalum, titanium and/or zirconium may be tolerated, the totalamount of these metals should in no event exceed 2% by weight,preferably 1%, and usually should be much less. Even smaller quantitiesof such elements as cobalt, nickel, copper, aluminum, beryllium, and/ orboron may 'be tolterated, the total in no event exceeding 1% by weight.Furthermore, the sum of the amounts of the carbide formers, chromium,molybdenum, vanadium, titanium and one-half of the amounts of tungsten,niobium, tantalum, and zirconium should be 12-165 preferably l316%. Itis preferred that no other carbide formers be present in addition tochromium, molybdenum and tungsten. As a rule, the carbon content shouldbe chosen within the narrower range 0.350.45%. Further the chromiumcontent should normally be held within the range 12l5 preferably 13-14%,and the silicon content should normally be at most 06%, and themanganese content at most 1.2%.

The carbon content has been chosen sufficiently high so that the steelcan attain a hardness of at least VPN 625 (test load 0.5 kg.) afterhardening and subzero cooling and possibly low temperature tempering,and at the same time so low that the steel is highly resistant to stresscorrosion failure. The content of chromium is so high that goodcorrosion resistance is obtained, but sufficiently low so that asatisfactory hardness can be attained after hardening. The content ofmolybdenum is usually chosen rather high to obtain good corrosionresistance, being from 0.5 to 2.0%, preferably from 0.8 to 1.5% when notungsten is present. While theoretically twice as much tungsten isneeded to obtain the same effect as molybdenum, it is usually advisableto avoid using the maxium quantity of tungsten and to confine its amountto 1.6 to 3.0% when no molybdenum is present. The sum of the amounts ofmolybdenum and one-half the tungsten, when both are present is 0.5 to2.0%, preferably 0.8 to 1.5%.

The steel for the razor blades according to the invention should permithardening to a high hardness in order to facilitate the grinding of thecutting edge or edges. Further the steel should be corrosion resistantand not liable to ruptures under the influence of chemical attack andsimultaneous bending. In order to achieve these properties the steelaccording to the composition defined has to be subject to a heattreatment especially adapted for the purpose.

The steel according to the invention should be heat treated in such away that absorption of nitrogen during the hardening is avoided, and forthis purpose the procedure should preferably be performed in a suitableprotective atmosphere, for instance pure hydrogen. In order to obtainthe best possible combination of flexibility, corrosion resistance,stress corrosion resistance and hardness the steel should be tempered ata temperature between 250 and 450 C., preferably 300-400 C.

The heat treatment includes an initial heating to a temperature between1000 and 1150 0, preferably l075 1100 C., followed by cooling to roomtemperature, usually between blocks cooled by water. This step may befollowed by subzero cooling to a temperature between 20 and 120 0.,usually 40 to -80 C., whereafter the steel preferably is tempered for ashort time at a temperature between 100 and 450 C., in order to obtain amaximal hardness exceeding VPN 625 (load 0.5 kg.). After this heattreatment the cutting edge or edges are prepared e.g. by shaping as bygrinding and then preferably a coating of the edge with a material forenhancing the shaving characteristics is applied and sintered to thesteel at a temperature between 250 and 450 C., e.g. at about 350 C.,resulting in a final hardness of about VPN 550 (load 0.5 kg).

The appended diagram comprises curves representing the susceptibility tosaid corrosion as a function of the carbon content for some differentsteel compositions, some of which are within and some without the scopeof the invention. Curve .A represent steels containing 13.5% Cr, whilethe curves B and C show steels according to the in vention containing13.5% Cr and 1.25% M0, the C steels having been melted in high vacuum.The steels in the form of thin cold-rolled strips have been heated at1075" C. during 30 seconds and have then been cooled to room temperatureand thereafter to 70 C. and have finally been tempered at 350 C. during15 minutes. The diagram shows that for steels having about 13.5% chromium and carbon contents Within the range 0.30-0.45 the sensitivity forstress corrosion is substantially lessened if molybdenum is added. Thediagram also shows that high vacuum treatment further decreases thesusceptibility to stress corrosion failures. It is thus advantageous tomelt the steel in high vacuum, as this further lessens the risk forruptures under the influence of stress corrosion conditions. However,this is not an absolute requirement. In the diagram the variation ofhardness in relation to the content of carbon is also noted.

In order further to increase the resistance to stress corrosion it is,as previously mentioned, desirable to have a low content of nitrogen. Itis also essential that the contents of phosphorous and sulphur be low. Apreferred range of analysis is the following: 0.35-0.45% carbon; 0.8-1.5molybdenum or twice this amount of tungsten; up to 0.6% silicon; up to1.2% manganese; 12.015.0% chromium; the balance being iron withinsignificant amounts of impurities, e.g. 50.025% phosphorus;

0.020% sulphur and 0.06% nitrogen Possibly minor quantities of otherconstituents as vanadium, titanium, niobium, tantalum, zirconium,aluminum, beryllium, boron, nickel, cobalt and copper, the total ofthese being at the most 1% may be included.

As a preferred range of analysis for steels according to the presentinvention the following can be mentioned: carbon=0.370.43%;molybdenum=l.11.4% (or twice this amount of tungsten) the sum of theamounts of molybdenum and one-half the tungsten being from 1.1-1.4%;chromium:13.0-14.0%; silicon=0.20.5%; manganese- 0.2-05 phosphorusg0.025%; sulphur 50.020%; nitrogen 50.06%; the balance beingsubstantially all iron.

As examples of alloys in percent of weight according to the inventionthe following may be mentioned:

Steel Si Mn Cr M0 P S NFe 0. 041 B alance. 0. 028 D 0.

4 final condition test pieces of the strip were subjected to a stresscorrosion test by bending to yield a surface tensile stress of 90,000p.s.i. and immersing in a 0.1% acetic acid solution at room temperaturefor 48 hours. No fractures occurred.

Steel 2 was treated in the same way but high vacuum remelted beforerolling down to a strip with the thickness of 0.0015". With the sameheat treatment as for steel No. 1 the hardness after the first temperingat 125 C. was VPN 690 and after the final tempering at 350 C. VPN 540.No fractures occurred at the stress corrosion test.

Although specific embodiments of the invention have been describedherein, it is not intended to limit the invention solely thereto but toinclude all of the variations and modifications which suggest themselvesto a person skilled in the art.

What is claimed is:

1. Razor blades and similar thin elongated sharp edged blades havinggood cutting properties and high corrosion resistance and toughnesscharacterized in that the blades are made from a steel consistingessentially of 0.35- 0.45% carbon; 12-15% chromium; a member of theclass consisting of molybdenum, tungsten and mixtures thereof, theamount of molybdenum when present alone being 0.8-1.5%, the amount oftungsten when present alone being 1.63.0%, and the sum of the amounts ofmolybdenum and one-half the tungsten when both are present being0.8-1.5% 00.6% silicon; 01.2% manganese; O1% each of a member of theclass consisting of vanadium, niobium, tantalum, titanium and zirconium,the total of all the last said members being a maximum of 1%; and 01%each of a member of the class consisting of cobalt, nickel, copper,aluminum, beryllium,

' and boron, the total of all the last said members being a maximum of1%; and the remainder being substantially all iron; and in which the sumof the amounts of chromium, molybdenum, vanadium, titanium and one-halfof the amounts of tungsten, niobium, tantalum and zirconium is 13-16%.

2. Razor blades as claimed in claim 1 in which the total amount of allvanadium, niobium, tantalum, titan ium, zirconium, cobalt, nickel,copper, aluminum, beryllium and boron is 01%.

3. Razor blades having good cutting properties, high corrosionresistance, and toughness characterized in that the blades are made froma steel which in addition to iron with incidental impurities consistsessentially of 0.37- 0.43% carbon; 1314% chromium; a member of the groupconsisting of molybdenum, tungsten and mixtures thereof, the amount ofmolybdenum when present alone being 1.1l.4%, the amount of tungsten whenpresent alone being 2.22.8%, and the sum of the amounts of molybdenumand one-half the tungsten when both are present being 1.11.4%; 0.20.5%silicon; and 02-05% manganese.

References Cited UNITED STATES PATENTS 2,853,410 9/1958 Lula 148313,116,180 12/1963 Malzacher 14812.4 2,105,583 1/1938 Casselman 30-346.542,513,935 7/1950 Harris 126(C) 2,648,602 8/1953 Payson 75126(C)2,905,577 9/1959 Harris 75126(C) 3,071,856 1/1963 Fischbein 30346.533,104,168 9/1963 Bedell 75126(C) 3,152,934 10/1964 Lula 75128.9

HYLAND BIZOT, Primary Examiner UJS. Cl. X.'R. 75126F

